The main causes of third-degree amniotic fluid contamination are increased gestational weeks, serious complications during pregnancy, and placental problems. 1. Increase in gestational weeks: Because the fetus can discharge meconium in the uterus to pollute the amniotic fluid, therefore, with the increase in gestational weeks, the meconium increases, and the chances of amniotic fluid contamination increase, and amniotic fluid contamination is commonly found in overdue pregnancies. 2. Serious complications in pregnancy: some complications in pregnancy, such as hypertensive disease of pregnancy, gestational diabetes, cholestasis syndrome in pregnancy lead to intrauterine hypoxia of the fetus, and meconium discharge increases, resulting in amniotic fluid contamination. 3. Placental problems: due to various reasons, the placenta is not mature enough and the blood supply to the fetus is insufficient, resulting in intrauterine hypoxia and increased meconium, leading to amniotic fluid contamination. It is recommended that pregnant women should go to the doctor on time for checkups, seek medical treatment in time if any complications are found, and pay attention to counting fetal movements in the late pregnancy, and consult a professional doctor in time if there is any abnormality.